Use endpoint argument to avoid collision with flask-admin Network

If a selectfield is disabled, None is returned (not a string).
To pass wtforms validation, that value shall be part of the choices.

We use None as the value for SelectField that are optional (instead of
'').
We were previously converting '' to None when creating a model.
We now use the coerce function to let the form convert 'None' to None.

- disable item field for virtual hosts
- pre-fill interface name with hostname

Description shall be filled at the host level

See http://docs.sqlalchemy.org/en/latest/core/compiler.html#utc-timestamp-function

TODO: we should be able to render HTML in the comments
Look at https://github.com/miguelgrinberg/Flask-PageDown

- Main blueprint used to declare custom views for all blueprints.
(keep inventory blueprint cleaner)
- Add url_prefix to each blueprint

See http://getbootstrap.com/docs/4.0/components/input-group/#button-addons

Those tokens are supposed to be used in scripts or applications to
access the API and should not expire.

Updated to flask-jwt-extended 3.4.0 to be able to disable expiration
See https://github.com/vimalloc/flask-jwt-extended/issues/105

Store some settings to the session to make it easy to register
several identical items.

In Flask, session data are stored in a cookie by default.
Using a server side session, there is no risk of putting too much data
in the session and transmissting a big cookie on every request
(only an id is sent in the cookie).

Redis is used as backend (without persistent storage).

main blueprint splitted in:
- inventory
- networks

- Rename Host to Interface
- Create new Host table to group interfaces

Use the session instead of URL parameters to store the last network
chosen.

There is no point displaying the LDAP groups in the profile

- All created tokens are stored in the database.
  To revoke a token, we just delete it from the database.
  Tokens not found in the database are thus considered unvalid / revoked.

- Add button to copy generated token to the clipboard

- Redesign profile page

See https://clipboardjs.com

Open source icon set with ready-to-use fonts for bootstrap
See https://useiconic.com/open/

hosttags table required for the many-to-many relationship
See http://flask-sqlalchemy.pocoo.org/2.3/models/#many-to-many-relationships

- Several IPs (hosts) can be associated to one MAC address
- Host name shall be non nullable

- refactor Network class

Catch exception when no network exists (null is passed as network_id).

- network name should be unique and not nullable
- force all name fields to StringField

Don't ovveride SQLAlchemy __init__ method on db.Model classes.

See http://flask-sqlalchemy.pocoo.org/2.3/quickstart/:
SQLAlchemy adds an implicit constructor to all model classes which
accepts keyword arguments for all its columns and relationships. If you
decide to override the constructor for any reason, make sure to keep
accepting **kwargs and call the super constructor with those **kwargs to
preserve this behavior